The present invention relates to novel acryl silicone base flow-and-leveling agents for powder coatings which can provide the coating surfaces with a flow-and-leveling property by adding them to powder coatings in small amounts.
In general powder coatings are inferior in a flow-and-leveling property on the coating surfaces, and therefore it has tended to be difficult to use them for applications in which high appearance is required. In recent years, however, it has been tried to use powder coatings in place of solvent base coatings for the purpose of environmental pollution measures. For example, it is investigated to use them for top coating for automobiles. This has required flow-and-leveling agents for powder coatings having high functions. Acryl base polymers, modified silicone oils and organic waxes have so far been used as flow-and-leveling agents in compliance with this requirement. Powdery flow-and-leveling agents of a hybrid type making use of acryl base polymers and organic waxes are proposed in, for example, Japanese Patent Publication No. 21977/1986.
The Problems to be Solved by the Invention
However, a satisfactory flow-and-leveling property are not necessarily obtained with these conventional techniques in the fields requiring a high appearance such as uses for automobiles which are researched in recent years, and when large amounts of flow-and-leveling agents are added in order to obtain a good appearance, adverse effects are exerted on a layer-to-layer adhesion in recoating or adverse effects such as roughening of the recoated films are often observed.
Accordingly, an object of the present invention is to provide flow-and-leveling agents capable of being utilized for uses requiring a high appearance which has not been obtained with conventional flow-and-leveling agents for powder coatings.
Means for Solving the Problems
Various investigations repeated by the present inventors have resulted in finding that a flow-and-leveling property which is so good as has never been can be provided onto the coating surface by blending powder coatings with flow-and-leveling agents of (1), (2), (3) and (4) described below and that adverse effects are not exerted on the recoating property.
(1) A flow-and-leveling agent for a powder coating comprising a trimethylsilyl group-containing copolymer obtained by copolymerizing a reactive monomer (A) having a trimethylsilyl group represented by a structural formula:
xe2x80x94Si(CH3)3
in a molecular structure and/or a reactive monomer (B) having a trimethylsilyl group in the form of a tris(trimethylsiloxy)silyl group represented by a structural formula:
xe2x80x94Si[OSi(CH3)3]3
in a molecular structure with a (meth)acrylic acid ester (C) represented by a formula: 
[wherein R1 represents a hydrogen atom or methyl, and R2 represents an alkyl group or alkenyl group having 1 to 18 carbon atoms] and/or a (meth)acrylic acid ester (D) represented by a formula: 
[wherein R3 represents a hydrogen atom or methyl; R4 represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms; n represents an integer of 2, 3 or 4, and m represents an integer of 1 to 50], wherein the above trimethylsilyl group-containing polymer contains a trimethylsilyl group originating in the monomers (A) and/or (B) in a proportion of 2 to 65% by weight, preferably 5 to 40% by weight and has a number average molecular weight of 1000 to 60000, preferably 2000 to 30000.
(2) A flow-and-leveling agent for a powder coating comprising a trimethylsilyl group-containing copolymer obtained by reacting a copolymer of a multifunctional monomer into which a trimethylsilyl group or a tris(trimethylsiloxy)silyl group can be introduced and the (meth)acrylic acid esters (C) and/or (D) described in the above item (1) with a trimethylsilyl group-containing compound and/or a tris(trimethylsiloxy)silyl group-containing compound, wherein the above trimethylsilyl group-containing polymer contains a trimethylsilyl group in a proportion of 2 to 65% by weight, preferably 5 to 40% by weight and has a number average molecular weight of 1000 to 60000, preferably 2000 to 30000.
(3) A flow-and-leveling agent for a powder coating comprising a trimethylsilyl group-containing copolymer obtained by copolymerizing the monomer (A) and/or (B) described in the above item (1) and the (meth)acrylic acid esters (C) and/or (D) described in the above item (1) with a reactive monomer (E) which can be copolymerized with them, wherein the above copolymer contains a trimethylsilyl group originating in the monomers (A) and/or (B) in a proportion of 2 to 65% by weight, preferably 5 to 40% by weight and a copolymerization unit originating in the monomer (E) in a proportion of not exceeding 50% by weight and has a number average molecular weight of 1000 to 60000, preferably 2000 to 30000.
(4) A flow-and-leveling agent for a powder coating comprising a trimethylsilyl group-containing copolymer obtained by reacting a copolymer of the multifunctional monomer described in the above item (2), the (meth)acrylic acid esters (C) and/or (D) described in the above item (1) and the reactive monomer described in the above item (3) with a trimethylsilyl group-containing compound and/or a tris(trimethylsiloxy)silyl group-containing compound, wherein the above trimethylsilyl group-containing copolymer contains a trimethylsilyl group in a proportion of 2 to 65% by weight, preferably 5 to 40% by weight and a copolymerization unit originating in the monomer (E) in a proportion of not exceeding 50% by weight and has a number average molecular weight of 1000 to 60000, preferably 2000 to 30000.
If a proportion of a trimethylsilyl group originating in the monomers (A) and/or (B) based on the copolymer is smaller than 2% by weight, the satisfactory flow-and-leveling property is not obtained. On the other hand, if it is more than 65% by weight, adverse effects are more likely to be exerted in recoating a coating film. When both the monomers (A) and (B) are used in combination, a proportion of the respective amounts thereof is optional, and they can be used in combination so that a proportion of a trimethylsilyl group based on the copolymer is 2 to 65% by weight.
The (meth)acrylic acid esters of the formulas (C) and/or (D) are copolymerized in order to provide an effect of obtaining a good flow-and-leveling property, and the satisfactory flow-and-leveling property can not be obtained with monomers other than them. When the number (m) of alkylene glycol units contained in the (meth)acrylic acid ester (D) exceeds 50, not only the satisfactory flow-and-leveling property can not be obtained, but also there is the concern that adverse effects in terms of the physical properties are exerted on the coating film. When both the monomers (C) and (D) are used in combination, a proportion of the respective amounts thereof is optional, and they can be used in combination so that a proportion of a trimethylsilyl group originating in the monomers (A) and/or (B) based on the copolymer is 2 to 65% by weight.
The copolymer of the (meth)acrylic acid esters (C) and/or (D) with the multifunctional monomer is subjected to addition reaction or condensation reaction with a trimethylsilyl group-condaining compound and/or a tris(trimethylsiloxy)silyl group-containing compound whereby a trimethylsilyl group can be introduced into the above copolymer. The copolymer obtained by this method provides as well the effect of endowing the coating surface with a good flow-and-leveling property if the trimethylsilyl group is introduced into the copolymer in a proportion of 2 to 65% by weight, preferably 5 to 40% by weight.
If the trimethylsilyl group is contained in the copolymer in a proportion of 2 to 65% by weight, preferably 5 to 40% by weight, an acryl silicone copolymer containing copolymerization units originating in the other reactive monomer (E) in a range in which the proportion based on the copolymer does not exceed 50% by weight provides as well the effect of endowing the coating surface with a good flow-and-leveling property.
If the copolymer has a number average molecular weight of smaller than 1000 or larger than 60000, the above copolymer does not have a sufficiently high ability to spread on a coating surface in coating, so that the satisfactory flow-and-leveling property can not be obtained.
The examples of the reactive monomer (A) having a trimethylsilyl group and the reactive monomer (B) having a trimethylsilyl group in the form of a tris(trimethylsiloxy)silyl group include 3-methacryloxypropyltrimethylsilane, 3-methacryloxypropyltris(trimethylsiloxy)silane, and vinyltris(trimethylsiloxy)silane. The examples of the trimethylsilyl group-condaining compounds and the tris(trimethylsiloxy)silyl group-containing compounds include trimethylchlorosilane, hexamethyldisilazane, tris(trimethylsiloxy)hydrosilane, 3-aminopropyltris(trimethylsiloxy)silane and 3-mercaptopropyltris(trimethylsiloxy)silane.
The (meth)acrylic acid alkyl or alkenyl ester (C) in which an alkyl group or an alkenyl group has 1 to 18 carbon atoms includes, for example, methyl (meth)acrylate, ethyl (meth)acrylate, normal propyl (meth)acrylate, isopropyl (meth)acrylate, normal butyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, normal octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, myristyl (meth)acrylate, hexadecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate and isobonyl (meth)acrylate.
The (meth)acrylic acid ester (D) includes 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-octoxyethyl (meth)acrylate, 2-lauroxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, ethylcarbitol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate [the number (m) of the ethylene glycol units is 1 to 50], methoxypolypropylene glycol (meth)acrylate [the number (m) of the propylene glycol units is 1 to 50], methoxypoly(ethylene-propylene)glycol (meth)acrylate [the total number (m) of the number of the ethylene glycol units and the number of the propylene glycol units is 2 to 50], methoxypoly(ethylene-tetramethylene)glycol (meth)acrylate [the total number (m) of the number of the ethylene glycol units and the number of the tetramethylene glycol units is 2 to 50], butoxypoly(ethylene-propylene)glycol (meth)acrylate [the total number (m) of the number of the ethylene glycol units and the number of the propylene glycol units is 2 to 50], octoxypoly(ethylene-propylene)glycol (meth)acrylate [the total number (m) of the number of the ethylene glycol units and the number of the propylene glycol units is 2 to 50], lauroxypolyethylene glycol (meth)acrylate [the number (m) of the ethylene glycol units is 1 to 50] and lauroxypoly(ethylene-propylene)glycol (meth)acrylate [the total number (m) of the number of the ethylene glycol units and the number of the propylene glycol units is 2 to 50].
The examples of the multifunctional monomer into which a trimethylsilyl group or a tris(trimethylsiloxy)silyl group can be introduced include, for example, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, 2-isocyanatoethyl (meth)acrylate, those in which R4 is a hydrogen atom in the formula representing the (meth)acrylic acid ester (D), allyl glycidyl ether, 2-hydroxyethyl vinyl ether and 4-hydroxybutyl vinyl ether.
The monomer (E) shall bot be restricted, and the examples thereof include, for example, (meth)acrylic acid esters other than (C) and (D) described above, such as behenyl (meth)acrylate and nonylphenoxypolyethylene glycol (meth)acrylate; acrylamides such as acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, diacetoneacrylamide and acryloylmorpholine; aromatic hydrocarbon base vinyl compounds such as styrene, xcex1-methylstyrene, chlorostyrene and vinyltoluene; vinyl esters or allyl compounds such as vinyl acetate, vinyl propionate and diallyl phthalate; vinyl ethers such as ethyl vinyl ether, normal propyl vinyl ether, isopropyl vinyl ether, normal butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, normal octyl vinyl ether, 2-ethylhexyl vinyl ether, methyl vinyl ether and cyclohexyl vinyl ether; vinyl chloride; vinylidene chloride; chloroprene; propylene; butadiene; isoprene; and fluoroolefinmaleimide.
A method for synthesizing the copolymer of the present invention includes an emulsion polymerization method, a suspension polymerization method, a solution polymerization method and a bulk polymerization method. Azo base polymerization initiators and peroxides are used as an initiator for carrying out polymerization.
Capable of being used as a method for introducing a trimethylsilyl group into the copolymer is a method in which polymerization reaction is carried out and then a compound having a trimethylsilyl group is added or condensed.
The present invention is an invention related to the functions of the copolymer and therefore shall by no means be restricted by the synthetic process of the copolymer.
Addition of the flow-and-leveling agents for powder coatings according to the present invention to coatings to which high appearance is required, for example, acryl powder coatings for automobile top coating and high appearance polyester melamine powder coatings for primarily home electric appliances PCM coating makes it possible to provide the coating surface with a sufficiently high flow-and-leveling property in coating and prevent ruptures and craters from being produced.
In respect to a method for adding the flow-and-leveling agents for powder coatings according to the present invention to the coatings, they are preferably added in preparing the coatings in the form of a master batch with the resins for the coatings or a powder mixture thereof with organic waxes.
An addition amount of the flow-and-leveling agents for powder coatings according to the present invention is varied depending on the kind of the resins for coatings and the blend compositions of pigments and is usually 0.01 to 5% by weight, preferably 0.1 to 2% by weight based on the coating vehicles in terms of the solid matters. If the addition amount is smaller than 0.01% by weight, the coating surface can not be provided with a sufficiently high flow-and-leveling property. On the other hand, if it is more than 5% by weight, adverse effects are more likely to be exerted on the physical properties of the coating film.
Effects of the Invention
The flow-and-leveling agent for a powder coating according to the present invention is a novel acryl silicone base copolymer and makes it possible to provide so good flow-and-leveling property as has never been without exerting adverse effects on the layer-to-layer adhesion in recoating.